Recording medium, information recording device, and information reproducing device

ABSTRACT

An information recording medium comprises a read-out track having a data region forming data bits for reproduced data and a servo pattern region forming servo bits for tracking control. The servo bits have a first groove that is deep in a direction perpendicular to both a length of the read-out track and a depth of the information recording medium, and a second groove that is deep in a direction opposite to the first groove and having a depth gradually increasing along the read-out track.

FIELD OF THE INVENTION

The present invention relates to an information recording medium fromwhich information can be reproduced by the utilization of near-fieldlight, and to an information reproducing apparatus for reproducinginformation recorded with on the information recording medium. Thepresent invention also relates to an information recording medium and toinformation reproducing apparatus by which tracking control is madepossible.

BACKGROUND OF THE INVENTION

Many of the existing information reproducing apparatuses reproduceinformation from magnetic disks or optical disks as informationrecording mediums. In particular, CDs, one of the optical disks, arebroadly utilized as media recording a large capacity of information dueto the capability of recording information with density and massproduction at low cost. The CD has, on its surface, pits formed having asize of nearly a wavelength of the laser light to be used in reproducingand a depth of approximately a quarter of the wavelength, enablingreading out utilizing interference phenomenon of light.

The lens optical systems generally used in the optical microscopes areutilized for reading recorded information out of the optical disksrepresentative of the CDs. Accordingly, where the pit size or trackpitch is reduced to increase information recording density, thelaser-light spot cannot be reduced in size to a half wavelength orsmaller due to the problem with optical diffraction limit, thus runningagainst a wall that the information recording unit is impossible toreduce to a size smaller than the laser-light wavelength.

Meanwhile, without limitation to the optical disks, the magneto-opticaldisks and DVDs recording information by the magneto-optical recordingscheme and phase-shift recording scheme realize recording/reproducing ofinformation with density due to laser-light microscopic spot.Consequently, the information recording density is limited to a spotsize obtained by focusing laser light.

In such circumstances, in order to break through such limitation due todiffraction limit, there is a proposal on an information reproducingapparatus using an optical head having a microscopic aperture having adiameter smaller than a wavelength of the laser light utilized inreproducing, e.g. nearly one-tenth thereof, to utilize near-field light(including both near field and far field) produced in the microscopicaperture.

Conventionally, as an apparatus utilizing near-field light, there hasbeen a near-field microscope using a probe having the above microscopicaperture which has been utilized for observing a microscopic surfacetexture of a sample. As one of the near-field light utilizing schemes inthe near-field microscope, there is a scheme (illumination mode) thatthe probe microscopic aperture and a sample surface are approached indistance to nearly a diameter of the probe microscopic aperture tointroduce propagation light through the probe and toward the probemicroscopic aperture thereby producing near-field light in themicroscopic aperture. In this case, the scattering light caused throughinteraction between the produced near-field light and the sample surfaceis detected, involving an intensity and phase reflecting sample-surfacefine texture, by a scattering-light detecting system. Thus, observationis made possible with a high resolving power never realized in theconvention optical microscopes.

Meanwhile, as another scheme of the near-field microscope utilizingnear-field light, there is a scheme (collection mode) that propagationlight is illuminated to a sample to localize near-field light on asample surface so that the probe microscopic aperture is approached tothe sample surface to a distance of nearly a diameter of the probemicroscopic aperture. In this case, the scattering light caused throughinteraction between the localized near-field light and the probemicroscopic aperture is guided, involving an intensity and phasereflecting sample-surface fine texture, to a scattering-light detectingsystem through probe microscopic aperture, achieving observation withhigh resolving power.

The foregoing information reproducing apparatus utilizing near-fieldlight makes use of these observation schemes for the near-fieldmicroscopes. By utilizing such near-field light, it is possible toreproduce information from the information recording medium havingrecord with density.

In order to realize reproducing of information recorded with density onan information recording medium by utilizing near-field light mentionedabove, a positioning control technology is required to accurately movethe probe microscopic aperture as an optical head to an arbitraryposition on the information recording medium.

In the magnetic disk : apparatuses, a servo-surface servo scheme and asector servo scheme are generally adopted for position control. Theservo-surface servo scheme is a method that one of a plurality of disksurfaces is used exclusively for servo so that a servo magnetic head ispositioned relative to this servo surface and the remaining disksurfaces and magnetic heads are used for data. Also, the sector servoscheme is a method that servo information is embedded here and there onthe data surface to use discretely-detected servo information therebypositioning the magnetic head to a data track.

However, it is difficult to apply the positioning control employed forthe magnetic disk apparatus to positioning control for reproducing witha high-density information medium due to near-field light. For example,because in the servo-surface servo scheme the servo head and the datahead are determined in position accuracy by mechanical accuracy, thereis a possibility of causing positional deviation between the both headsdue to a difference in temperature distribution, thus making it improperto employ as positioning control to an information recording medium withespecial density in the information reproducing apparatus utilizingnear-field light.

Meanwhile, the above sector servo scheme is free from occurrence ofpositional deviation of the head by the difference in temperaturedistribution as is rendered problematic in the servo-surface servoscheme. However, in a control-system design stage, there is a need tohandle as a discrete-value system different from the conventionalcontinuous system. Because the information reproducing apparatusutilizing near-field light requires accurate positioning to anespecially dense information recording medium, devising is needed forusing such a complicated control system.

On the other hand, the optical disk apparatus employs a positioningcontrol method, particularly as tracking error detecting method, athree-beam method, a push-pull method, a pre-wobbling tracking errordetecting method. The three-beam method is a method that the beam from alaser diode is divided by a diffraction grating into totally three beamsof 0-order light (main beam) for recording and reproducing, ±1-orderlight (sub-beams) of two in number and two sub-beams are slightlydeviated from a center of a guide groove provided on an optical disk sothat reflection light from the both is received by two light-receivingsurfaces of a photo-detector to provide a differential signal thereoffor controlling the objective lens.

Also, the push-pull method is a method that the reflection light of abeam illuminated to a guide groove provided on an optical disk isdetected in a two-division detector to thereby obtain a differentialsignal as a tracking error signal for controlling the objective lens.The pre-wobbling tracking error detecting method is a method thatelongate pits (wobbling marks) A and B, each set thereof comprising two,are arranged relative to a center of the track radially of the disk withslight deviation relative to a center of the track so that, when thelight spot traces a center of the track, a change in the amount of thereflection light from the pits A and B is caused as a tracking errorsignal to control the objective lens.

The above-explained tracking error detection methods for the opticaldisk apparatus in any thereof are the methods wherein the illuminationlight to the pits formed on the disk and the reflection light reflectedby them are both handled as propagation light (far field). Devising hasbeen required where applied for detecting non-propagation light (nearfield) such as near-field light or reflection scattering light thereof.In particular, in the information recording medium that reproduction ispossible with utilization of near-field light, information recordingunit could have been determined by a difference in optical propertybesides concave-convex information such as pits formed on theconventional optical disk. There has been a desire for optical-headpositioning control for reproducing from such an information recordingmedium, particularly an information reproducing apparatus for performingtracking.

It is an object of the present invention to provide, in view of theabove problems, an information recording medium and informationreproducing apparatus for reproducing information with reliability foran information recording medium having dense record, particularlyrealizing tracking by a simple structure.

SUMMARY OF THE INVENTION

In order to achieve the above object, a first information recordingmedium of the present invention is, in an information recording mediumforming, on a medium surface, information to be reproduced by areproducing probe having a microscopic aperture for producing near-fieldlight, characterized in that: a reproduced-data zone recordingreproduced data and a servo pattern zone recording servo data fortracking control are provided on a read-out track to be read by thereproducing probe; as the servo data being arranged alternately a firstgroove formed having a depth increased constantly or gradually in onedirection perpendicular to both a direction of the read-out track and adirection of a depth of the medium and a second groove formed having adepth increased constantly or gradually in the other directionperpendicular to both the direction of the read-out track and thedirection of the depth of the medium, on the read-out track in the servopattern zone.

According to this invention, prepared as the servo data for trackingcontrol are a first groove formed having, a depth increased constantlyor gradually in one direction perpendicular to both a direction of theread-out track and a direction of a depth of the medium and a secondgroove made reverse in depth increase direction to the first groove,which are alternately arranged on the read-out track in the servopattern zone. Accordingly, where near-field light is introduced to theread-out track of the servo data in a position deviated from a centerthereof, it is possible to obtain reflection scattering light withrepeating high and low intensities. This can be utilized as a signal fortracking control.

Also, a second information recording medium of the present invention ischaracterized, in the first information recording medium, in that thefirst groove and second groove are triangular in section taken in thedirection perpendicular to the read-out track.

According to this invention, because the section of the servo data in adirection perpendicular to the read-out direction is made in atriangular form, it is possible to provide a smooth and slant surfacefor the servo data. Where introducing near-field light, it is possibleto obtain reflection scattering light finely varying in the depthdirection.

Also, a third information recording medium of the present invention ischaracterized, in the first information recording medium, in that thefirst groove and second groove are stepwise in section taken in thedirection perpendicular to the read-out track.

According to this invention, because the section of the servo data in adirection perpendicular to the read-out direction is made in a stepwiseform, it is possible to obtain reflection scattering light varyingstepwise where near-field light is introduced to the servo data in eachposition in a direction away from a center thereof.

Also, a fourth information recording medium of the present invention is,in an information recording medium forming, on a medium surface,information to be reproduced by a reproducing probe having a microscopicaperture for producing near-field light, characterized in that: areproduced-data zone recording reproduced data and a servo pattern zonerecording servo data for tracking control are provided on a read-outtrack to be read by the reproducing probe; as the servo data beingarranged alternately a first groove formed having an interval in adirection of the read-out track increased constantly or gradually in onedirection perpendicular to both the direction of the read-out track anda direction of a depth of the medium and a second groove formed havingan interval in the direction of the read-out track increased constantlyor gradually in the other direction perpendicular to both the directionof the read-out track and the direction of the depth of the medium, onthe read-out track in the servo pattern zone.

According to this invention, prepared as the servo data for trackingcontrol are a first groove formed having an interval increasedconstantly or gradually in one direction perpendicular to both adirection of the read-out track and a direction of a depth of the mediumand a second groove made reverse in interval increase direction to thefirst groove, which are alternately arranged on the read-out track inthe servo pattern zone. Accordingly, where near-field light isintroduced to the read-out track of the servo data in a positiondeviated from a center thereof, it is possible to obtain reflectionscattering light with repeating high and low intensities. This can beutilized as a signal for tracking.

Also, a fifth information recording medium of the present invention is,in an information recording medium forming, on a medium surface,information to be reproduced by a reproducing probe having a microscopicaperture for producing near-field light, the information recordingmedium, characterized in that: a unit of the information comprises agroove formed having a depth constantly or gradually increased in onedirection perpendicular to both a direction of a read-out track to beread by the reproducing probe and a direction of a depth of the medium.

According to this invention, a unit of the information is constituted bya groove formed having a depth constantly or gradually increased in onedirection perpendicular to both a direction of a read-out track to beread by the reproducing probe and a direction of a depth of the medium.Accordingly, when reading out the information, where near-field light isintroduced from a center of this read-out track to each positionperpendicular to the read-out track and in a plane direction of themedium, it is possible to obtain reflection scattering light differentin intensity. This can be utilized as a signal for tracking.

Also, a sixth information recording medium of the present invention is,in an information recording medium forming, on a medium surface,information to be reproduced by a reproducing probe having a microscopicaperture for producing near-field light, the information recordingmedium characterized in that: a section taken in a directionperpendicular to a read-out direction to be read by the reproducingprobe is formed in the form of saw tooth, the information being formedalong a slant surface constituting the saw tooth.

According to this invention, a section taken in a directionperpendicular to a read-out direction to be read by the reproducingprobe is formed in the form of saw tooth, and each slant surfaceconstituting the saw tooth is formed with the information as a read-outtrack. Accordingly, when reading out the information, where near-fieldlight is introduced from a center of this read-out track to eachposition perpendicular to the read-out track and in a plane direction ofthe medium, it is possible to obtain reflection scattering lightdifferent in intensity. This can be utilized as a signal for tracking.

Also, a first information reproducing apparatus of the present inventionis, in an information reproducing apparatus for reproducing informationby a reproducing probe having a microscopic aperture for producingnear-field light, characterized by comprising: an information recordingmedium having on a read-out track to be read by the reproducing probe areproduced-data zone recording reproduced data and a servo pattern zonerecording servo data for tracking control, the servo data being arrangedwith a constant deviation alternately left and right with respect to acenter axis of the read-out track; photo-detecting means for detectingreflection scattering light caused due to scattering of the near-fieldlight by the servo data and outputting a detection signal; comparisonoperating means for comparing between a detection signal outputted fromthe photo-detecting means and a synchronization signal determined basedon an interval of the servo data and generating and outputting adifferential signal; and reproducing-probe-position control means forcontrolling a position of the reproducing probe according to thedifferential signal.

According to this invention, an information recording medium is providedwith a reproduced-data zone recording reproduced data and a servopattern zone recording servo data for tracking control. The servo datais arranged with a constant deviation alternately left and right withrespect to a center axis of the read-out track. By making incident thenear-field light produced in the microscopic aperture of the reproducingprobe on the servo pattern zone, it is possible to obtain a trackingsignal having a waveform different depending on a deviation from acenter axis of the read-out track. Because the reproducing probe iscontrolled in position according to the tracking detection signal,accurate tracking control utilizing near-field light is made possible.

Also, a second information reproducing apparatus of the presentinvention is, in an information reproducing apparatus for reproducinginformation by a reproducing probe having a microscopic aperture forproducing near-field light, characterized by comprising: an informationrecording medium having on a read-out track to be read by thereproducing probe a reproduced-data zone recording reproduced data and aservo pattern zone recording servo data for tracking control, as theservo data being arranged alternately a first groove formed having adepth increased constantly or gradually in one direction perpendicularto both a direction of the read-out track and a direction of a depth ofthe medium and a second groove formed having a depth increasedconstantly or gradually in the other direction perpendicular to both thedirection of the read-out track and the direction of the depth of themedium, on the read-out track in the servo pattern zone; photo-detectingmeans for detecting reflection scattering light caused due to scatteringof the near-field light by the servo data and outputting a detectionsignal; comparison operating means for comparing between a detectionsignal outputted from the photo-detecting means and a synchronizationsignal determined based on an interval of the servo data and generatingand outputting a differential signal; and reproducing-probe-positioncontrol means for controlling a position of the reproducing probeaccording to the differential signal.

According to this invention, an information recording medium is providedwith a reproduced-data zone recording reproduced data and a servopattern zone recording servo data for tracking control. Prepared as theservo data are a first groove formed having a depth increased constantlyor gradually in one direction perpendicular to both a direction of theread-out track and a direction of a depth of the medium and a secondgroove formed reverse in depth increasing direction to the first groove,which are alternately arranged on the read-out track in the servopattern zone. By making incident the near-field light produced in themicroscopic aperture of the reproducing probe on the servo pattern zone,it is possible to obtain a tracking signal having a different waveformdue to a deviation from a center axis of the read-out track. Because thereproducing probe is controlled in position according to the trackingdetection signal, accurate tracking control utilizing near-field lightis made possible.

Also, a third information reproducing apparatus of the present inventionis, in an information reproducing apparatus for reproducing informationby a reproducing probe having a microscopic aperture for producingnear-field light, characterized by comprising: an information recordingmedium having on a read-out track to be read by the reproducing probe areproduced-data zone recording reproduced data and a servo pattern zonerecording servo data for tracking control, as the servo data beingarranged alternately a first groove formed having an interval in adirection of the read-out track increased constantly or gradually in onedirection perpendicular to both the direction of the read-out track anda direction of a depth of the medium and a second groove formed havingan interval in the direction of the read-out track increased constantlyor gradually in the other direction perpendicular to both the directionof the read-out track and the direction of the depth of the medium, onthe read-out track in the servo pattern zone; photo-detecting means fordetecting reflection scattering light caused due to scattering of thenear-field light by the servo data and outputting a detection signal;comparison operating means for comparing between a detection signaloutputted from the photo-detecting means and a synchronization signaldetermined based on an interval of the servo data and generating andoutputting a differential signal; and reproducing-probe-position controlmeans for controlling a position of the reproducing probe according tothe differential signal.

According to this invention, an information recording medium is providedwith a reproduced-data zone recording reproduced data and a servopattern zone recording servo data for tracking control. Prepared as theservo data are a first groove formed having an interval in a directionof the read-out track increased constantly or gradually in one directionperpendicular to both the direction of the read-out track and adirection of a depth of the medium and a second groove formed having aninterval in the direction of the read-out track increased constantly orgradually in the other direction perpendicular to both the direction ofthe read-out track and the direction of the depth of the medium. Theseare alternately arranged on the read-out track in the servo patternzone. By making incident the near-field light produced in themicroscopic aperture of the reproducing probe on the servo pattern zone,it is possible to obtain a tracking detection signal having a waveformdifferent depending on a deviation from a center axis of the read-outtrack. Because the reproducing probe is controlled in position accordingto the tracking detection signal, accurate tracking control utilizingnear-field light is made possible.

Also, a fourth information reproducing apparatus of the presentinvention is, in an information reproducing apparatus for reproducinginformation by a reproducing probe having a microscopic aperture forproducing near-field light, characterized by comprising: an informationrecording medium forming a unit of the information as a groove formedhaving a depth constantly or gradually increased in one directionperpendicular to both a direction of a read-out track to be read by thereproducing probe and a direction of a depth of the medium;photo-detecting means for detecting reflection scattering light causeddue to scattering of the near-field light by the servo data andoutputting a detection signal; and reproducing-probe-position controlmeans for controlling a position of the reproducing probe according tothe differential signal.

According to this invention, an information recording medium forms, as aunit of the information, a groove formed having a depth constantly orgradually increased in one direction perpendicular to both a directionof a read-out track to be read by the reproducing probe and a directionof a depth of the medium. Accordingly, when reading out the information,the intensity of the near-field light interacting with this information,i.e. a tracking detection signal detected in the photo-detector, variesin a position deviated from a center axis of the read-out track.Consequently, it is possible to control a position of the reproducingprobe according to an intensity of the tracking detection signal andperforming accurate tracking control utilizing near-field light.

Also, a fifth information reproducing apparatus of the present inventionis, in an information reproducing apparatus for reproducing informationby a reproducing probe having a microscopic aperture for producingnear-field light, characterized by comprising: an information recordingmedium in which a section taken in a direction perpendicular to aread-out direction to be read by the reproducing probe is formed in, theform of saw tooth, the information being formed along a slant surfaceconstituting the saw tooth; photo-detecting means for detectingreflection scattering light caused due to scattering of the near-fieldlight by the servo data and outputting a detection signal; andreproducing-probe-position control means for controlling a position ofthe reproducing probe according to the intensity of the detectionsignal.

According to this invention, an information recording medium is formedwith a section taken in a direction perpendicular to a read-outdirection to be read by the reproducing probe is formed-in the form ofsaw tooth. The information along a slant surface as a read-out trackconstituting the saw tooth. Accordingly, when reading out theinformation, the intensity of the near-field light interacting with thisinformation, i.e. a tracking detection signal detected in thephoto-detector, varies in a position deviated from a center axis of theread-out track. Consequently, it is possible to control a position ofthe reproducing probe according to an intensity of the trackingdetection signal and performing accurate tracking control utilizingnear-field light.

Also, a sixth information reproducing apparatus of the present inventionis, in an information reproducing apparatus for reproducing informationby a reproducing probe having a microscopic aperture for producingnear-field light, characterized by comprising: an information recordingmedium forming the information on a read-out track to be read by thereproducing probe; a reproducing probe having microscopic aperturesformed having an interval in a direction of the read-out track increasedconstantly or gradually in one direction perpendicular to both adirection of the read-out track and a direction of a depth of themedium; photo-detecting means for detecting reflection scattering lightcaused due to scattering of the near-field light by the information andoutputting a detection signal; and reproducing-probe-position controlmeans for controlling a position of the reproducing probe according toan intensity of the refection scattering signal.

According to this invention, a reproducing probe has microscopicapertures made in a form having an interval in a direction of theread-out track increased constantly in a direction of the read-outtrack. Accordingly, the intensity of the near-field light interactingwith the information formed on the information recording medium, i.e. atracking detection signal detected in the photo-detector, varies in aposition deviated from a center axis of the read-out track.Consequently, it is possible to control a position of the reproducingprobe according to an intensity of the tracking detection signal andperforming accurate tracking control utilizing near-field light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a schematic structure of aninformation reproducing apparatus according to the present invention.

FIG. 2 is a figure showing the recorded bits of an information recordingmedium according to Embodiment 1.

FIG. 3 is a figure showing the recorded bits of an information recordingmedium according to Embodiment 2.

FIG. 4 is a figure explaining the recorded bits of the informationrecording medium according to Embodiment 2.

FIG. 5 is a figure explaining the operation of an information recordingapparatus according to Embodiment 2.

FIG. 6 is a figure explaining the operation of the information recordingapparatus according to Embodiment 2.

FIG. 7 is a figure explaining the operation of the information recordingapparatus according to Embodiment 2.

FIGS. 8(a) and 8(b) show other examples of the recorded bits of aninformation recording medium according to Embodiment 2.

FIG. 9 is a figure showing the recorded bits of an information recordingmedium according to Embodiment 3.

FIG. 10 is a figure explaining the recorded bits of an informationrecording medium according to Embodiment 4.

FIG. 11 is a figure explaining the recorded bits and read-out track ofan information recording medium according to Embodiment 5.

FIG. 12 is a figure explaining a reproducing probe of an informationrecording apparatus according to Embodiment 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of information recording mediums and information reproducingapparatuses according to the present invention will be explained indetail below based on the drawings.

(Embodiment 1)

FIG. 1 is a block diagram showing a schematic structure of aninformation reproducing apparatus according to Embodiment 1 of thepresent invention. In FIG. 1, the information reproducing apparatusaccording to Embodiment 1 is structured by a reproducing probe 1 forreproducing near-field light, an information recording medium 3 formingrecorded bits (including both data bit for reproducing data and servobits for tracking control) with density, photo-detectors 6 and 7 forreceiving the reflected scattering light scattered by the recorded bits4 on the information recording medium 3 and outputting electric signals,an add circuit 10 for amplifying each electric signal outputted from thephoto-detectors 6 and 7 to perform add operation and outputting additionsignals, a detection-signal extracting circuit 11 for extracting areproduced signal and a tracking detection signal related to trackingcontrol from the addition signal outputted from the add circuit 10 andoutputting them, a reproduced-data output circuit 12 for acquiring andoutputting reproduced data outputted from the detection-signalextracting circuit 11, a tracking-signal producer 13 for producing andoutputting a tracking signal from a tracking detection signal outputtedfrom the detection-signal extracting circuit 11, and an actuator 14 forcontrolling the position of the reproducing probe in accordance with atracking signal outputted from the tracking-signal producer 13.

In the reproducing probe 1, a microscopic aperture 2 is formed having adiameter in a size smaller than a wavelength of the laser light 8introduced from a laser light source (not shown), e.g. several tenth ofnano-meters. Near-field light 5 is produced in the microscopic aperture2 by introducing the laser light 8. In FIG. 1, as a reproducing probe 1is shown a planar probe having photo-detectors 6 and 7 provided in aplanar substrate forming an inverted conical or pyramidal penetrationhole to provide a microscopic aperture 2 in an apex thereof. However, aprobe used in the usual near-field microscope can be utilized in placethereof. For example, it is possible to utilize an probe capable ofproducing near-field light in an illumination mode as described before,including an optical fiber probe comprising an optical fiber having amicroscopic aperture at a tip and coated with metal over a surface and acantilever-type optical probe having at a tip a microscopic aperture toguide laser light through an optical waveguide. However, in this case,there is a need to independently arrange the photo-detector togetherwith an optical lens system in the vicinity of the probe.

The near-field light 5 produced in the microscopic aperture 2 of thereproducing probe 1 is scattered by the recorded bits 4 formed on theinformation recording medium 3, whose scatter light turns intopropagation light (hereinafter, referred to as reflection scatter light)and introduced to the photo-detectors 6 and 7. Herein, the planar probeas shown in FIG. 1 is fabricated by a silicon process as used in theconventional semiconductor producing technology. The photo-detectors 6and 7 are photo-diodes integrated on a silicon wafer. Meanwhile, wherethe photo-detectors 6 and 7 are independently arranged as describedabove, the photo-detectors 6 and 7 are photo-diodes, photo-electronicmultiplying tubes or the like.

FIG. 2 is a figure showing recorded bits on the information recordingmedium 3 to be reproduced in the information reproducing apparatusaccording to Embodiment 1. In FIG. 2, the information recording medium 3is provided, on a track to be read out by the reproducing probe 1, witha data region forming data bits for reproduced data and a servo-patternregion forming servo bits for tracking control. In the data region, thedata bits 22 are arranged in a predetermined information pattern suchthat a center axis thereof coincides with a center axis 20 of theread-out track. On the other hand, in the servo pattern region, theservo bits 21 are formed alternately left and right with respect to thecenter axis 20 of the read-out track. In this manner, the informationrecording medium 3 adopts the foregoing sector servo scheme and formservo bits 21 serving a pre-wobbling mark as servo information thereof.Note that, in this information recording medium 3, there is a need toprovide comparatively large a spacing Tp between the read-out tracksbecause the servo bits are arranged alternately left and right withrespect to the center axis 20 of the read-out track.

The operation of the information reproducing apparatus according toEmbodiment 1 will be explained below on the assumption that the recordedbits are read out by the reproducing probe 1 by making the informationrecording medium 3 in a disk form and rotating it at its center by arotary mechanism (not shown). First, in the case that reading out ismade in a state the microscopic aperture 2 of the reproducing probe 1 ata center is along the center axis 20 of the read-out track on theinformation recording medium 3, i.e. where the center axis 20 of theread-out track is positioned on an area that the near-field light 5produced in the microscopic aperture 2 is maximum in intensity, thereflection scatter light of the near-field light 5 obtained due toscatter by the data bits 22 in the data region exhibits sufficientlyhigh intensity. Accordingly, it is possible to obtain reliablereproduced signals in accordance with the recording pattern of the databits 22 through the photo-detectors 6 and 7.

On the other hand, the reflection scatter light of the near-field light5 obtained due to scatter by the servo bits 21 in the servo patternregion also outputs a tracking detection signal in accordance with therecord pattern of the servo bits 21 through the photo-detectors 6 and 7.Herein, the record pattern of the servo bits 21 is formed at a certainconstant interval throughout the entire read-out track in the servopattern region. Consequently, when the reproducing probe 1 passes theservo pattern region, a tracking detection signal is outputted with aperiod determined by a reading rate (rotation velocity of theinformation recording medium 3) from the photo-detectors 6 and 7. Inparticular, because the servo bits 21 are arranged, with even deviation,alternately left and right with respect to the center axis 20 of thetrack, where reading out is made in a state the center of themicroscopic aperture 2 of the reproducing probe 1 is along the centeraxis 20 of the read-out track on the information recording medium 3, theintensity of a tracking detection signal to be obtained on each servobit is equal.

Next, in the case that reading out is made in a state the microscopicaperture 2 of the reproducing probe 1 at a center is deviated off thecenter axis 20 of the read-out track on the information recording medium3, i.e. where the center axis 20 of the read-out track is positioneddeviated off an area that the near-field light 5 produced in themicroscopic aperture 2 is maximum in intensity, the reflection scatterlight of the near-field light 5 obtained due to scatter by the data bits22 in the data region does not exhibit sufficiently high intensity.Accordingly, in order to obtain a reproduced signal that the informationpattern of the data bits 22 is positively reproduced throughphoto-detectors 6 and 7, there is a need of tracking control to move thereproducing probe 1 to the center axis 20 of the read-out track.

On the other hand, the tracking detection signal obtained for the servobit 21 deviated toward off the reproducing probe 1 exhibits highintensity while the tracking detection signal for the servo bit 21positioned deviated in the reverse direction exhibits low intensity.Accordingly, when the reproducing probe 1 passes the servo patternregion, outputted is a tracking detection signal having a waveformalternately repeating high and low intensities.

Herein, the electric signal (reproduced signal and tracking detectionsignal) outputted from the photo-detectors 6 and 7 is subjected at alltimes to amplification and add operation in the add circuit 10 andoutputted as an add signal to the detection-signal extracting circuit11. In the detection-signal extracting circuit 11, determination is madeas to whether the reproducing probe at present is passing the dataregion or the servo pattern region, by the use of a synchronizationsignal with a period determined by a reading rate (rotation velocity ofthe information recording medium 3). In the case that the reproducingprobe 1 is passing the data region, the add signal outputted from theadd circuit 10 is inputted as a reproduced signal to the reproduced-dataoutput circuit 12. Where the reproducing probe 1 is passing the servopattern region, the add signal outputted from the add circuit 10 isinputted as a tracking detection signal to the tracking signal producer13.

As described above, where reading out is made in the state that thecenter of the microscopic aperture 2 of the reproducing probe 1 is offthe center axis 20 of the read-out track of the information recordingmedium 3 and a tracking signal having a waveform alternately repeatinghigh and low intensities is inputted to the tracking signal producer 13,the tracking signal reproducer 13 first compares the waveformrepresented by the tracking detection signal, particularly the magnitudeof signals for the beginning two servo bits in the servo pattern region.Depending on the relationship in magnitude, it is determined whether thereproducing probe 1 at present is deviated toward an inner peripheralside or an outer peripheral side of the information recording medium 3.Further, by operating an intensity difference between the signals, atracking signal is produced that represents a moving direction andmoving amount of the reproducing probe 1. This tracking signal isoutputted to the actuator 14. In the actuator 14, the reproducing probeis moved depending on the tracking signal outputted from the trackingsignal reproducer 13, thereby achieving tracking control.

As explained above, according to the information recording mediumaccording to Embodiment 1, on the read-out track are provided a dataregion forming data bits for reproduction data and a servo patternregion forming servo bits for tracking control. Furthermore, the servobits in the servo pattern region are arranged with alternate deviationsof left and right from the center axis of the read-out track.Accordingly, it is possible to provide a tracking detection signal fortracking control. Also, according to the information recording apparatusaccording to Embodiment 1, in the servo pattern region of theinformation recording medium, a tracking detection signal can beobtained that has a waveform different depending upon a deviation of thecenter axis of the read-out track. From a waveform pattern of thistracking detection signal, tracking control can be made for thereproducing probe. Also, because the near-field light produced in themicroscopic aperture of the reproducing probe is utilized as a signalfor tracking control, accurate tracking control is achieved with highpositional resolving power. Furthermore, because the optical system usedfor reproduced-signal detection and tracking-signal detection isintegrated without separation, the apparatus structure can besimplified.

(Embodiment 2)

Next, explained is an information reproducing apparatus according toEmbodiment 2. Because the schematic structure of the informationreproducing apparatus according to Embodiment 2 is similar to FIG. 1explained in Embodiment 1, the explanation thereof is herein omitted.The difference of the information reproducing apparatus according toEmbodiment 2 from Embodiment 2 lies in that the servo bits formed in aservo pattern region on the information recording medium 3 are arrangedin series on a center axis of a read-out track and the form of the servobit is not symmetric left and right about the center line of theread-out track.

FIG. 3 is a figure showing recorded bits on the information recordingmedium 3 to be reproduced in the information reproducing apparatusaccording to Embodiment 2. In FIG. 3, the information recording medium 3is provided, on a track to be read out, with a data region forming databits for reproduced data and a servo-pattern region forming servo bitsfor tracking control. In the data region, the data bits 22 are arrangedin a predetermined information pattern such that a center axis thereofcoincides with a center axis 20 of the read-out track of the reproducingprobe 1. On the other hand, in the servo pattern region, the servo bits30 and 31 are formed at a constant interval such that the center axisthereof coincides with the center axis 20 of the read-out track of thereproducing probe 1, similarly to the data bits 22.

Herein, the servo bit 30 and 31 is asymmetric left and right about thecenter axis 20 of the read-out track in a depth direction of theinformation recording medium 3, and particularly a groove having a depthconstantly increased in one direction. Furthermore, the servo bit 30 andthe servo bit 31 are arranged alternately on the center axis 20 of theread-out track and with difference in a direction of the left-and-riftasymmetric form. FIG. 4 is a sectional view of the servo bits 30 and 31in a radial direction of the information recording medium 3. In FIG. 4,provided that the left side of the page is given as an inner-diameterdirection of the information recording medium 3 and the right side ofthe page is given as an outer-diameter direction of the informationrecording medium 3, the servo bit 30 as shown in FIG. 4(a) is a groovehaving a triangular section increasing in depth in the inner-diameterdirection. Also, the servo bit 31 as shown in FIG. 4(b) is a groovehaving a triangular section increasing in depth in the outer-diameterdirection of the information recording medium 3. In particular, theservo bit 30 and the servo bit 31 are arranged on the center axis 20 ofthe read-out track such that they are equal in center depth.Incidentally, in this information recording medium 3, because the servobits are arranged on the center axis of the read-out track, the spacingTp′ between the read-out track can be made comparatively small thusimproving record density.

The operation of the information reproducing apparatus according toEmbodiment 2 will be explained below on the assumption that the recordedbits are read out by the reproducing probe 1 by making the informationrecording medium 3 in a disk form and rotating it at its center by arotary mechanism (not shown). First, in the case that reading out ismade in a state the microscopic aperture 2 of the reproducing probe 1 ata center is along the center axis 20 of the read-out track on theinformation recording medium 3, i.e. where the center axis 20 of theread-out track is positioned on an area that the near-field light 5produced in the microscopic aperture 2 is maximum in intensity, thereflection scatter light of the near-field light 5 obtained due toscatter by the data bits 22 in the data region exhibits sufficientlyhigh intensity. Accordingly, it is possible to obtain reliablereproduced signals in accordance with the recording pattern of the databits 22 through the photo-detectors 6 and 7.

FIG. 5 is a figure for explaining a position of the reproducing probe 1in the servo pattern region in the above case (FIG. 5(a)) and a trackingdetection signal detected in the photo-detectors 6 and 7 (FIG. 5(b)). InFIG. 5(b), tracking detection signals 40 and 41 respectively correspondto tracking detection signals obtained from the servo bits 30 and 31.Incidentally, the reflection scatter light of the near-field light 5obtained through scattering by the servo bits 30 and 31 is alsooutputted as tracking detection signals through the photo-detectors 6and 7. Herein, the servo bits 30 and 31 are alternately formed at aconstant interval throughout the read-out track in the servo patternregion. Consequently, when the reproducing probe 1 passes the servopattern region, from the photo-detectors 6 and 7 is outputted a trackingdetection signal with a period determined by a reading rate (rotationvelocity of the information recording medium 3). Particularly, the servobits 30 and 31 are made equal in depth on the track center axis 20 toeach other. Accordingly, as shown in FIG. 5(a), where reading out ismade in a state that the microscopic aperture 2 of the reproducing probe1 at a center is along the center axis 20 of the read-out track of theinformation recording medium 3, tracking detection signals 40 and 41obtained for the servo bits 30 and 31 are equal in intensity as shown inFIG. 5(b).

Next, in the case that reading out is made in a state the microscopicaperture 2 of the reproducing probe 1 at the center is deviated off thecenter axis 20 of the read-out track on the information recording medium3, i.e. where the center axis 20 of the read-out track is positioneddeviated off an area that the near-field light 5 produced in themicroscopic aperture 2 is maximum in intensity, the reflection scatterlight of the near-field light 5 obtained due to scattering by the databits 22 in the data region does not exhibit sufficiently high intensity.Accordingly, in order to obtain a reproduced signal that the informationpattern of the data bits 22 is positively reproduced through thephoto-detectors 6 or 7, there is a need of tracking control to move thereproducing probe 1 to the center axis 20 of the read-out track.

FIG. 6 is a figure for explaining a state that the reproducing probe 1is deviated toward the outer diameter of the information recordingmedium 3 with respect to the read-out track (FIG. 6(a)) and a trackingdetection signal detected in the photo-detectors 6 and 7 (FIG. 6(b)).Note that, in FIG. 6, the upper side of the page is given as the outerdiameter direction of the information recording medium 3 while the lowerside of the page is given as the inner diameter direction of theinformation recording medium 3. In FIG. 6(b), tracking detection signals40 and 41 are respectively correspond to the signals obtained from theservo bits 30 and 31. Herein, the near-field light 5 exhibits anintensity distribution that the intensity decreases as the distanceincreases from the microscopic aperture 2 of the reproducing probe 1.Consequently, as in FIG. 6(a), the near-field light 5 in a position thereproducing probe 1 deviates toward the outer diameter of thereproducing probe 1 is scattered in a shallower position in the servobit 30 and in a deeper position in the servo bit 31. That is, thetracking detection signal 40 obtained from the servo bit 30 exhibits agreater value than the tracking detection signal 41 obtained from theservo bit 31, as shown in FIG. 6(b).

FIG. 7 is a figure for explaining a state that, conversely to the FIG. 6case, the reproducing probe 1 is deviated toward the inner diameter ofthe information recording medium 3 with respect to the read-out track(FIG. 7(a)) and a tracking -detection signal detected in thephoto-detectors 6 and 7 (FIG. 7(b)). Note that, in FIG. 7, the upperside of the page is given as the inner-diameter direction of theinformation recording medium 3 while the lower side of the page is givenas the outer-diameter direction of the information recording medium 3.In FIG. 7(b), tracking detection signals 40 and 41 are respectivelycorrespond to the signals obtained from the servo bits 30 and 31. Asshown in FIG. 7, the near-field light 5 in a position where thereproducing probe 1 deviates toward the outer diameter is scattered in adeeper position in the servo bit 30 and in a shallower position in theservo bit 31. That is, the tracking detection signal 41 obtained fromthe servo bit 31 exhibits a greater value than the tracking detectionsignal 40 obtained from the servo bit 30, as shown in FIG. 7(b).

As explained above, when reproducing probe 1 passes the servo patternregion in a state the microscopic aperture 2 at its center of thereproducing probe 1 is off the center axis 20 of the read-out track onthe information recording medium 3, outputted is a tracking detectionsignal having a waveform alternately repeating high and low intensities.

Herein, the electric signal (reproduced signal and tracking detectionsignal) outputted from the photo-detectors 6 and 7 is at all timessubjected to amplification and add operation in the add circuit 10 andoutputted as an add signal to the detection-signal extracting circuit11. In the detection-signal extracting circuit 11, determination is madeas to whether the reproducing probe 1 at present is passing the dataregion or the servo pattern region, by the use of a synchronizationsignal with a period determined by a reading rate (rotation velocity ofthe information recording medium 3). In the case that the reproducingprobe 1 is passing the data region, the add signal outputted from theadd circuit 10 is inputted as a reproduced signal to the reproduced-dataoutput circuit 12. Where the reproducing probe 1 is passing the servopattern region, the add signal outputted from the add circuit 10 isinputted as a tracking detection signal to the tracking signal producer13.

As described above, where reading out is made in the state that thecenter of the microscopic aperture 2 of the reproducing probe 1 is offthe center axis 20 of the read-out track and a tracking detection signalhaving a waveform alternately repeating high and low intensities isinputted to the tracking signal producer 13, the tracking signalreproducer 13 first compares the waveform represented by the trackingdetection signal, particularly the magnitude of signals for thebeginning two servo bits in the servo pattern region. Depending on therelationship in magnitude, it is determined whether the reproducingprobe 1 at present is deviated toward an inner peripheral side or anouter peripheral side of the information recording medium 3. Further, byoperating an intensity difference between the signals, a tracking signalis produced that represents a moving direction and moving amount of thereproducing probe 1 and this tracking signal is outputted. In theactuator 14, the reproducing probe is moved depending on the trackingsignal outputted from the tracking signal reproducer 13, therebyachieving tracking control.

That is, in this tracking control, as shown in FIG. 6(a), in a statethat the reproducing probe 1 deviates in the outer-diameter direction ofthe information recording medium 3 with respect to the read-out track,the reproducing probe 1 is moved toward the inner diameter of theinformation recording medium 3 to the center axis of the read-out track.As shown in FIG. 7(a), in a state that the reproducing probe 1 deviatesin the inner-diameter direction of the information recording medium 3with respect to the read-out track, the reproducing probe 1 is movedtoward the outer diameter of the information recording medium 3 to thecenter axis of the read-out track.

Incidentally, in Embodiment 2 explained above, the servo bits wereformed in the servo pattern region of the information recording medium 3such that its section is of a triangular groove. In place of this, asshown in FIGS. 8(a) and 8(b), grooves 50 and 51 may be formed stepwisein radial section of the information recording medium 3.

As explained above, according to the information recording mediumaccording to Embodiment 2, on the read-out track are provided a dataregion forming data bits for reproduction data and a servo patternregion forming servo bits for tracking control. Furthermore, as servobits in the servo pattern region are arranged grooves that areasymmetric left and right about the center axis of the read-out trackand have a depth constantly increased, alternately on the center axis ofthe read-out track and differently in direction of the left-and-rightasymmetric form from one another. Accordingly, it is possible to providea tracking detection signal for tracking control from a difference inservo-bit depth in a position deviated from the center axis of theread-out track. Also, according to the information recording apparatusaccording to Embodiment 2, in the servo pattern region of theinformation recording medium, a tracking detection signal can beobtained that has a waveform different depending upon a deviation of thecenter axis of the read-out track. From a waveform pattern of thistracking detection signal, tracking control can be made for thereproducing probe. Also, because the near-field light produced in themicroscopic aperture of the reproducing probe is utilized as a signalfor tracking control, accurate tracking control is achieved with highpositional resolving power. Furthermore, because the optical system usedfor reproduced-signal detection and tracking-signal detection isintegrated without separation, the apparatus structure can besimplified.

(Embodiment 3)

Next, an information reproducing apparatus according to Embodiment 3 isexplained. Because the schematic structure of an information reproducingapparatus according to Embodiment 3 is similar to FIG. 1 explained inEmbodiment 1, the explanation thereof is herein omitted. The informationreproducing apparatus according to Embodiment 3 has servo bits, formedin a servo pattern region in the information recording medium 3 inEmbodiment 2, having a shape in asymmetric in a plane direction about acenter axis of the read-out track.

FIG. 9 is a figure showing recorded bits on the information recordingmedium 3 to be reproduced in the information reproducing apparatusaccording to Embodiment 3. In FIG. 9, the information recording medium 3is provided, on a track to be read out by the reproducing probe 1, witha data region forming data bits for reproduced data and a servo-patternregion forming servo bits for tracking control. In the data region, thedata bits 22 are arranged in a predetermined information pattern suchthat a center axis thereof coincides with a center axis 20 of theread-out track. On the other hand, in the servo pattern region, theservo bits 36 and 37 are formed at a constant interval such that acenter axis thereof coincides with the center axis 20 of the read-outtrack of the reproducing probe 1 similarly to the data bits 22.

Herein, the servo bits 36 and 37 are in a form asymmetric left andright, e.g. in a triangular form, about the center axis 20 of theread-out track in a plane direction of the information recording medium3, and particularly, grooves having an interval constantly increased ina track direction. Furthermore, the servo bit 36 and the servo bit 37are arranged alternately different in direction of the left-and-rightasymmetric form on the center axis 20 of the read-out track. Inparticular, the servo bit 36 and the servo bit 37 are arranged such thattheir positions mutually equal in interval in a track direction are madecoincident with the center axis 20 of the read-out track. Incidentally,because in the information recording medium 3 the servo bits arearranged on the center axis of the read-out track, the read-out-trackspacing Tp′ can be given comparatively small, improving record density.

The operation of the information reproducing apparatus according toEmbodiment 3 will be explained below on the assumption that the recordedbits are read out by the reproducing probe 1 by making the informationrecording medium 3 in a disk form and rotating it at its center by arotary mechanism (not shown). First, in the case that reading out ismade in a state the microscopic aperture 2 of the reproducing probe 1 ata center is along the center axis 20 of the read-out track on theinformation recording medium 3, i.e. where the center axis 20 of theread-out track is positioned on an area that the near-field light 5produced in the microscopic aperture 2 is maximum in intensity, thereflection scatter light of the near-field light 5 obtained due toscattering by the data bits 22 in the data region exhibits sufficientlyhigh intensity. Accordingly, it is possible to obtain reproduced signalsin accordance with the recording pattern of the data bits 22 through thephoto-detectors 6 and 7.

Herein, the servo bits 36 and 37 are alternately formed at a certainconstant interval throughout the entire read-out track in the servopattern region. Consequently, when the reproducing probe 1 passes theservo pattern region, a tracking detection signal is outputted with aperiod determined by a reading rate (rotation velocity of theinformation recording medium 3) from the photo-detectors 6 and 7. Inparticular, because the servo bits 36 and 37 are arranged equal ininterval on the center axis 20 of the track, where reading out is madein a state the center of the microscopic aperture 2 of the reproducingprobe 1 is along the center axis 20 of the read-out track on theinformation recording medium 3, the intensity of a tracking signal to beobtained on the servo bits 36 and 37 is equal.

Next, in the case that reading out is made in a state the microscopicaperture 2 of the reproducing probe 1 at a center is deviated off thecenter axis 20 of the read-out track on the information recording medium3, i.e. where an area that the near-field light 5 produced in themicroscopic aperture 2 is maximum in intensity is deviated from thecenter axis 20 of the read-out track, the reflection scatter light ofthe near-field light 5 obtained due to scattering by the data bits 22 inthe data region does not exhibit sufficiently high intensity.Accordingly, in order to obtain a reproduced signal that the informationpattern of the data bits 22 is positively reproduced through thephoto-detectors 6 and 7, there is a need of tracking control to move thereproducing probe 1 to the center axis 20 of the read-out track.

Incidentally, where a scattering object exists in a near-field lightdistribution produced from the microscopic aperture 2, the near-fieldlight 5 causes reflection scatter light having an intensity dependentupon the size of the scattering object. In FIG. 9, provided that theupper side of the page is in the outer-diameter direction of theinformation recording medium 3 while the lower side of the page is inthe inner-diameter direction of the information recording medium 3, thenear-field light 5 in a position deviated toward the inner diameter ofthe reproducing probe 1 is scattered more in the servo bit 36 and lessin the servo bit 37. That is, the tracking detection signal obtainedfrom the servo bit 36 exhibits a greater value than the trackingdetection signal obtained from the servo bit 37.

Meanwhile, conversely to the above case, the near-field light 5 in aposition the reproducing probe 1 is deviated toward the outer diameterof the information recording medium 3 with respect to the read-out trackis scattered more in the servo bit 37 and less in the servo bit 36. Thatis, the tracking detection signal obtained from the servo bit 37exhibits a greater value than the tracking detection signal obtainedfrom the servo bit 36.

As explained above, when the reproducing probe 1 passes the servopattern region in a state that the microscopic aperture 2 of thereproducing probe 1 at the center deviates from the center axis 20 ofthe read-out track of the information recording medium 3, outputted is atracking detection signal having a waveform alternately repeating highand low intensities.

Herein, the electric signal (reproduced signal and tracking detectionsignal) outputted from the photo-detectors 6 and 7 is subjected at alltimes to amplification and add operation in the add circuit 10 andoutputted as an add signal to the detection-signal extracting circuit11. In the detection-signal extracting circuit 11, determination is madeas to whether the reproducing probe at present is passing the dataregion or the servo pattern region, by the use of a synchronizationsignal with a period determined by a reading rate (rotation velocity ofthe information recording medium 3). In the case that the reproducingprobe 1 is passing the data region, the add signal outputted from theadd circuit 10 is inputted as a reproduced signal to the reproduced-dataoutput circuit 12. Where the reproducing probe 1 is passing the servopattern region, the add signal outputted from the add circuit 10 isinputted as a tracking detection signal to the tracking signal producer13.

As described above, where reading out is made in the state that thecenter of the microscopic aperture 2 of the reproducing probe 1 is offthe center axis 20 of the read-out track of the information recordingmedium 3 and a tracking signal having a waveform alternately repeatinghigh and low intensities is inputted to the tracking signal producer 13,the tracking signal reproducer 13 first compares the waveformrepresented by the tracking detection signal, particularly the magnitudeof signals for the beginning two servo bits in the servo pattern region.Depending on the relationship in magnitude, it is determined whether thereproducing probe 1 at present is deviated toward an inner peripheralside or an outer peripheral side of the information recording medium 3.Further, by operating an intensity difference between the signals, atracking signal is produced that represents a moving direction andmoving amount of the reproducing probe 1. This tracking signal isoutputted to the actuator 14. In the actuator 14, the reproducing probeis moved depending on the tracking signal outputted from the trackingsignal reproducer 13, thereby achieving tracking control.

Incidentally, although in the Embodiment 3 explained above the servobits were formed as grooves made in a triangular form in its planedirection, stepwise grooves in place of this may be formed in the planedirection. Furthermore, instead of the grooves, they may be formed usingmarks having a shape that the interval in a track direction isconstantly increased in one direction (material having a property thatthe ratio with which near-field light is scattered is locally different,particularly the refractive index differs from the surrounding).

As explained above, according to the information recording mediumaccording to Embodiment 3, on the read-out track are provided a dataregion forming data bits for reproduction data and a servo patternregion forming servo bits for tracking control. Furthermore, arranged asservo bits in the servo pattern region are grooves in a form asymmetricleft and right about the center axis 20 of the read-out track and aninterval increased in the track direction, alternately on the centeraxis of the read-out track and differently in direction of theleft-and-right asymmetric form from one another. Accordingly, it ispossible to provide a tracking detection signal for tracking controlfrom a difference in servo-bit interval in a position deviated from thecenter axis of the read-out track. Also, according to the informationrecording apparatus according to Embodiment 3, in the servo patternregion of the information recording medium, a tracking detection signalcan be obtained that has a waveform different depending upon a deviationof the center axis of the read-out track. From a waveform pattern ofthis tracking detection signal, tracking control can be made for thereproducing probe. Also, because the near-field light produced in themicroscopic aperture of the reproducing probe is utilized as a signalfor tracking control, accurate tracking control is achieved with highpositional resolving power. Furthermore, because the optical system usedfor reproduced-signal detection and tracking-signal detection isintegrated without separation, the apparatus structure can besimplified.

(Embodiment 4)

Next, an information reproducing apparatus according to Embodiment 4 isexplained. Because the schematic structure of an information reproducingapparatus according to Embodiment 4 is similar to FIG. 1 explained inEmbodiment 1, the explanation thereof is herein omitted. The informationreproducing apparatus according to Embodiment 4 is not formed with servobits for tracking control on the information recording medium 3 butdevised in data bits form to obtain reproduced data from the data bitsand acquire a tracking detection signal for tracking control.

FIG. 10 is a figure showing recorded bits on the information recordingmedium 60 to be reproduced in the information reproducing apparatusaccording to Embodiment 4. In FIG. 10(a), the information recordingmedium 60 has, on a track to be read out by the reproducing probe 1,data bits 62 for reproduction data arranged in an information pattern toshow reproduction data with a center axis thereof coincided with acenter axis 61 of the read-out track. Herein, the data bits 62 are in aform asymmetric left and right about the center axis 61 of the read-outtrack in a depth direction of the information recording medium 60,particularly in grooves having a depth constantly increased in onedirection. Furthermore, the data bits 62 are arranged on the center axis61 of the read-out track with their left-and-right asymmetric formaligned in direction. FIG. 10(b) shows a section in A-A′ of FIG. 10(a),wherein the data bit 62 is triangular in section as shown in FIG. 10(b).

The operation of the information reproducing apparatus according toEmbodiment 4 will be explained below on the assumption that data bitsare read out by the reproducing probe 1 by making the informationrecording medium 60 in a disk form and rotating it at its center by arotary mechanism (not shown). First, in a state the microscopic aperture2 of the reproducing probe 1 at a center is along the center axis 61 ofthe read-out track on the information recording medium 60, thereflection scatter light of the near-field light 5 obtained due toscattering by the data bits 62, i.e. the intensity of an electric signalobtained in the photo-detectors 6 and 7, is previously stored as areference value in a storage section (not shown) of the detection-signalextracting circuit 11. This reference value represents a detectionsignal for the data bit where reading out is made by the reproducingprobe 1 in a correct position.

Next, explanation is made on a case that reading out is made in a statethe microscopic aperture 2 of the reproducing probe 1 at the center isdeviated from the center axis 61 of the read-out track on theinformation recording medium 60, i.e. positioned with deviation are anarea where the near-field light 5 produced in the microscopic aperture 2is maximum in intensity and the center axis 61 of the read-out track. InFIG. 10(a), provided that the upper side of the page is in anouter-diameter direction of the information recording medium 60 whilethe lower side of the page is in an inner-diameter direction of theinformation recording medium 60, the near-field light 5 exhibits anintensity distribution that the intensity decreases as the distanceincreases from the microscopic aperture 2 of the reproducing probe 1.Accordingly, for example, the near-field light 5 in a position deviatedtoward the outer-diameter is scattered at a deeper position in the databit 62. That is, the tracking detection signal obtained from the databit 62 exhibits a value smaller than the reference value.

Conversely, the near-field light 5 in a position the reproducing probe 1is deviated toward the inner-diameter is scattered at a shallowerposition in the data bit 62. That is, the tracking detection signalobtained from the data bit 62 exhibits a value greater than thereference value.

Herein, the electric signal (reproduced signal and tracking detectionsignal) outputted from the photo-detectors 6 and 7 is subjected at alltimes to amplification and add operation in the add circuit 10 andoutputted as an add signal to the detection-signal extracting circuit11. In the detection-signal extracting circuit 11, the add signaloutputted from the add circuit 110 is outputted as a reproduced signalto the reproduced-data output circuit 12, and comparison-operated withthe reference value and inputted as a tracking detection signalincluding a difference value and symbol to the tracking signal producer13.

As described above, where reading out is made in the state that themicroscopic aperture 2 of the reproducing probe 1 at its center is offthe center axis 61 of the read-out track on the information recordingmedium 3, a tracking signal representative of a moving direction andmoving amount of the reproducing probe 1 is first produced in thetracking signal producer 13 from a difference value and symbolrepresented by the tracking detection signal, and this tracking signalis outputted to the actuator 14. In the actuator 14, the reproducingprobe 1 is moved depending on the tracking signal outputted from thetracking signal producer 13 thereby achieving tracking control.

That is, in this tracking control, in the state that the reproducingprobe 1 is deviated toward the outer diameter of the informationrecording medium 60 with respect to the read-out track, the reproducingprobe 1 is moved toward the inner diameter of the information recordingmedium 60 up to the center axis of the read-out track. In the state thatthe reproducing probe 1 is deviated toward the inner diameter of theinformation recording medium 60 with respect to the read-out track, thereproducing probe 1 is moved toward the outer diameter of theinformation recording medium 60 up to the center axis of the read-outtrack.

Incidentally, in Embodiment 4 explained above, the data bits were formedsuch that its section is in a triangular groove. In place of this, theymay be formed such that the section in a radial direction of theinformation recording medium 3 is in a stepwise groove. Furthermore,instead of forming asymmetric-formed grooves in a depth direction,formed may be grooves having a form that the interval in a trackdirection is constantly increased in a plane direction or marks(material having a property locally different in ratio of scatteringnear-field light such that the refractive index is different from thatof the surrounding).

As explained above, according to the information recording mediumaccording to Embodiment 4, formed as data bits are grooves, that arenon-symmetric left and right about the center axis 61 of the read-outtrack and having a depth constantly increased in one direction areprepared and deployed direction of their depth that right and left arenon-symmetric. Accordingly, it is possible to provide a trackingdetection signal for tracking control from the difference in data-bitdepth in a position deviated from the center axis of the read-out track.Also, according to the information reproducing apparatus according toEmbodiment 4, tracking signals can be obtained that have an intensitydifferent depending upon a deviation of the center axis of the read-outtrack. From a comparison between the intensity of the tracking detectionsignal and the predetermined reference value, tracking control can bemade for the reproducing probe. Also, because the near-field lightproduced in the microscopic aperture of the reproducing probe isutilized for a signal for tracking control, accurate tracking control isachieved with positional resolving power. Furthermore, because theoptical systems used in reproduced-signal detection and tracking-signaldetection are integrated without separation, the apparatus structure canbe simplified.

(Embodiment 5)

Next, an information reproducing apparatus according to Embodiment 5 isexplained. Because the schematic structure of an information reproducingapparatus according to Embodiment 5 is similar to FIG. 1 explained inEmbodiment 1, the explanation thereof is herein omitted. The informationreproducing apparatus according to Embodiment 5 is not formed with servobits for tracking control on the information recording medium but has aread-out track itself slant in one direction to form data bits on theread-out track.

FIG. 11 is a figure showing data bits on the information recordingmedium 70 to be reproduced in the information reproducing apparatusaccording to Embodiment 5. In FIG. 11(a), the information recordingmedium 70 has, on a track to be read out by the reproducing probe 1,data bits 72 for reproduction data arranged in an information pattern toshow reproduction data with a center axis thereof coincided with acenter axis 71 of the read-out track. Herein, each read-out track isslanted at a constant angle in one direction. That is, the section inB-B′ of FIG. 11(a) is in a saw-tooth form as in FIG. 11(b). The slantsurface of each saw tooth is made for a read-out track to form data bitsalong the slant surface.

The operation of the information reproducing apparatus according toEmbodiment 5 will be explained below on the assumption that data bitsare read out by the reproducing probe 1 by making the informationrecording medium 70 in a disk form and rotating it at its center by arotary mechanism (not shown). First, in a state the microscopic aperture2 of the reproducing probe 1 at a center is along the center axis 71 ofthe read-out track on the information recording medium 70, thereflection scatter light of the near-field light 5 obtained due toscattering by the data bits 72, i.e. the intensity of an electric signalobtained in the photo-detectors 6 and 7, is previously stored as areference value in a storage section (not shown) of the detection-signalextracting circuit 11. This reference value represents a detectionsignal for the data bit where reading out is made by the reproducingprobe 1 in a correct position.

Next, explanation is made on a case that reading out is made in a statethe microscopic aperture 2 of the reproducing probe 1 at the center isdeviated from the center axis 71 of the read-out track on theinformation recording medium 70, i.e. positioned with deviation are anarea where the near-field light 5 produced in the microscopic aperture 2is maximum in intensity and the center axis 71 of the read-out track. InFIG. 11(a), provided that the upper side of the page is in anouter-diameter direction of the information recording medium 70 whilethe lower side of the page is in an inner-diameter direction of theinformation recording medium 70, the near-field light 5 exhibits anintensity distribution that the intensity decreases as the distanceincreases from the microscopic aperture 2 of the reproducing probe 1.Accordingly, for example, the near-field light 5 in a position of thereproducing probe 1 deviated toward the outer-diameter is scattered at ashallower position on the slant surface of the read-out track formingthe data bits 72. That is, the tracking detection signal obtained fromthe data bit 72 exhibits a value greater than the reference value.

Conversely, the near-field light 5 in a position the reproducing probe 1is deviated toward the inner-diameter of the information recordingmedium 70 is scattered at a deeper position on the slant surface of theread-out track forming the data bit 72. That is, the tracking detectionsignal obtained from the data bit 72 exhibits a value smaller than thereference value.

Herein, the electric signal (reproduced signal and tracking detectionsignal) outputted from the photo-detectors 6 and 7 is subjected at alltimes to amplification and add operation in the add circuit 10 andoutputted as an add signal to the detection-signal extracting circuit11. In the detection-signal extracting circuit 11, the add signaloutputted from the add circuit 10 is outputted as a reproduced signal tothe reproduced-data output circuit 12, and comparison-operated with thereference value and inputted as a tracking detection signal including adifference value and symbol to the tracking signal producer 13.

As described above, where reading out is made in the state that themicroscopic aperture 2 of the reproducing probe 1 at its center is offthe center axis 71 of the read-out track on the information recordingmedium 70, a tracking signal representative of a moving direction andmoving amount of the reproducing probe 1 is first produced in thetracking signal producer 13 from a difference value and symbolrepresented by the tracking detection signal, and this tracking signalis outputted to the actuator 14. In the actuator 14, the reproducingprobe 1 is moved depending on the tracking signal outputted from thetracking signal producer 13 thereby achieving tracking control.

That is, in this tracking control, in the state that the reproducingprobe 1 is deviated toward the outer diameter of the informationrecording medium 70 with respect to the read-out track, the reproducingprobe 1 is moved toward the inner diameter of the information recordingmedium 70 up to the center axis of the read-out track. In the state thatthe reproducing probe 1 is deviated toward the inner diameter of theinformation recording medium 70 with respect to the read-out track, thereproducing probe 1 is moved toward the outer diameter of theinformation recording medium 70 up to the center axis of the read-outtrack.

Incidentally, in Embodiment 5 explained above, the data bits 72 areformed as grooves or marks (material having a property locally differentin scatter ratio of near-field light e.g. different in refractive indexfrom the surroundings) on the read-out track.

As explained above, according to the information recording mediumaccording to Embodiment 5, slant is provided in one direction for eachread-out track. Accordingly, a tracking detection signal for trackingcontrol can be provided from a depth difference of data bits in aposition deviated from the center axis of the read-out track. Also,according to the information reproducing apparatus according toEmbodiment 5, tracking signals can be obtained that have an intensitydifferent depending upon a deviation of the center axis of the read-outtrack. From a comparison between the intensity of the tracking detectionsignal and the predetermined reference value, tracking control can bemade for the reproducing probe. Also, because the near-field lightproduced in the microscopic aperture of the reproducing probe isutilized as a signal for tracking control, accurate tracking control isachieved with high positional resolving power. Furthermore, because theoptical systems used in reproduced-signal detection and tracking-signaldetection are integrated without separation, the apparatus structure canbe simplified.

(Embodiment 6)

Next, an information reproducing apparatus according to Embodiment 6 isexplained. Because the schematic structure of an information reproducingapparatus according to Embodiment 6 is similar to FIG. 1 explained inEmbodiment 1, the explanation thereof is herein omitted. The informationreproducing apparatus according to Embodiment 6 is not formed with servobits for tracking control but formed only with data bits on theinformation recording medium whereby devising is made on the shape of amicroscopic aperture of the reproducing probe.

FIG. 12 is a figure showing recorded bits on the information recordingmedium 80 to be reproduced and a reproducing probe 83 in the informationreproducing apparatus according to Embodiment 6. In FIG. 12(a), theinformation recording medium 80 has, on a read-out track, data bits 82for reproduction data arranged in an information pattern to showreproduction data with a center axis thereof coincided with a centeraxis 81 of the read-out track of the reproducing probe.

Herein, the microscopic aperture 84 of the reproducing probe 83 isasymmetric left and right about the center axis 81 of the read-out trackin a plane direction of the information recording medium 80,particularly, in a shape constantly increased in interval in a trackdirection in one direction as shown in FIG. 12(a).

The operation of the information reproducing apparatus according toEmbodiment 6 will be explained below on the assumption that data bitsare read out by the reproducing probe 83 by making the informationrecording medium 80 in a disk form and rotating it at its center by arotary mechanism (not shown). First, in a state the microscopic aperture84 of the reproducing probe 83 at a center is along the center axis 81of the read-out track on the information recording medium 80, thereflection scatter light of the near-field light 5 obtained due toscattering by the data bits 82, i.e. the intensity of an electric signalobtained in :the photo-detectors 6 and 7, is previously stored as areference value in a storage section (not shown) of the detection-signalextracting circuit 11. This reference value represents a detectionsignal for the data bit where reading out is made by the reproducingprobe 83 in a correct position.

Next, explanation is made on a case that reading out is made in a statethe microscopic aperture 84 of the reproducing probe 83 at the center isdeviated from the center axis 81 of the read-out track on theinformation recording medium 80. In FIG. 12(a), provided that the upperside of the page is in an outer-diameter direction of the informationrecording medium 80 while the lower side of the page is in aninner-diameter direction of the information recording medium 80, thenear-field light 5 exhibits an intensity distribution that the intensityincreases as the spacing increases. Accordingly, production is made withhigher intensity in the outer diameter side of the information recordingmedium 80 while with lower intensity in the inner diameter side of theinformation recording medium 80. Consequently, in a position of thereproducing probe 83 deviated toward the outer diameter, reflectionscatter light in smaller magnitude is obtained in the data bit 82. Thatis, the tracking detection signal obtained from the data bit 82 exhibitsa value smaller than the reference value.

Conversely, in a position of the reproducing probe 83 deviated towardthe inner diameter, reflection scatter light in greater magnitude isobtained in the data bit 82. That is, the tracking detection signalobtained from the data bit 82 exhibits a value greater than thereference value.

Herein, the electric signal (reproduced signal and tracking detectionsignal) outputted from the photo-detectors 6 and 7 is subjected at alltimes to amplification and add operation in the add circuit 10 andoutputted as an add signal to the detection-signal extracting circuit11. In the detection-signal extracting circuit 11, the add signaloutputted from the add circuit 10 is outputted as a reproduced signal tothe reproduced-data output circuit 12, and comparison-operated with thereference value and inputted as a tracking detection signal including adifference value and symbol to the tracking signal producer 13.

As described above, where reading out is made in the state that themicroscopic aperture 84 of the reproducing probe 83 at its center isdeviated from the center axis 81 of the read-out track on theinformation recording medium 80, a tracking signal representative of amoving direction and moving amount of the reproducing probe 83 is firstproduced and outputted in the tracking signal producer 13 from adifference value and symbol represented by the tracking detectionsignal. In the actuator 14, the reproducing probe is moved depending onthe tracking signal outputted from the tracking signal producer 13thereby achieving tracking control.

That is, in this tracking control, in the state that the reproducingprobe 83 is deviated toward the outer diameter of the informationrecording medium 80 with respect to the read-out track, the reproducingprobe 83 is moved toward the inner diameter of the information recordingmedium 80 up to the center axis of the read-out track. In the state thatthe reproducing probe 83 is deviated toward the inner diameter of theinformation recording medium 80 with respect to the read-out track, thereproducing probe 83 is moved toward the outer diameter of theinformation recording medium 80 up to the center axis of the read-outtrack.

Incidentally, in Embodiment 6 explained above, the data bits 82 areformed as grooves or marks (material having a property locally differentin scatter ratio of near-field light e.g. different in refractive indexfrom the surroundings) on the read-out track.

As explained above, according to the information recording mediumaccording to Embodiment 6, because the microscopic aperture of thereproducing probe is made in a shape that the spacing in the read-outtrack is constantly increased in one direction, a tracking detectionsignal for tracking control can be obtained from a difference inintensity of near-field light interacting with the data bit in aposition deviated from the center axis of the read-out track. From acomparison between the intensity of the tracking detection signal andthe predetermined reference value, tracking control can be made for thereproducing probe. Also, because the near-field light produced in themicroscopic aperture of the reproducing probe is utilized for a signalfor tracking control, accurate tracking control is achieved with highpositional resolving power. Furthermore, because the optical systemsused in reproduced-signal detection and tracking-signal detection areintegrated without separation, the apparatus structure can besimplified.

In Embodiments 1 to 6 explained above, although data was read out bymaking the information recording medium in a disk form and rotating itat high velocity, the information recording medium may be made in aplanar plate instead of the disk form to read out data due to vectorscan of the reproducing probe.

In Embodiments 1 to 3 and 5 to 6 explained above, explanation was madeon the information recording medium and information reproducingapparatus for performing tracking control during informationreproducing. However, also in the case of recording information to aninformation recording medium using phase-shift film, there is a need toconduct tracking control similarly to the case during informationreproducing. In such a case, similarly to the shown in Embodiments 1 to3 and 5 to 6 as above, it is needless to say that tracking control canbe done by making asymmetric, with respect to a track direction, any ofthe arrangement or shape of servo data, track sectional form andaperture shape.

In Embodiment 1 to 3 explained above, explanation was made on the casethat servo bits having asymmetry with respect to the track directionwere alternately arranged on a center axis of the track. However, it isneedless to say that they may be not necessarily alternate butsatisfactorily arranged in a predetermined pattern.

In Embodiments 1 to 6 explained above, concerning asymmetry in the servobits and data bits, track and aperture form, various forms such astrapezoid may be satisfactory only if having asymmetry with respect to atrack direction besides triangular, stepwise and saw-tooth forms.

In Embodiments 1 to 6 explained above, although the electric signal fromthe photo-detectors 6 and 7 was amplified and added in the add circuit10, the amplification and addition are not necessarily performed. Forexample, where the photo-detectors 6 and 7 are integral, addition is notrequired. Also, where the electric signal is high in S/N, there is noneed to perform particular amplification. Furthermore, it is needless tosay that the differential signal may be as a tracking detection signal.

INDUSTRIAL APPLICABILITY

As explained above, according to the first information recording medium,prepared as the servo data are a first groove formed having a depthincreased constantly or gradually in one direction perpendicular to botha direction of the read-out track and a direction of a depth of themedium and a second groove made reverse in depth increase direction tothe first groove, which are alternately arranged on the read-out trackin the servo pattern zone. Accordingly, where near-field light isintroduced to the read-out track of the servo data in a positiondeviated from a center thereof, it is possible to obtain reflectionscattering light with repeating high and low intensities. This can beutilized as a signal for tracking control.

According to the second information recording medium of the presentinvention, the following is given in addition to the effect in the firstinformation recording medium. Because the section of the servo data in adirection perpendicular to the read-out direction is made in atriangular form, it is possible to provide a slant surface for the servodata. Where introducing near-field light, it is possible to obtainreflection scattering light finely varying in the depth direction.

According to the third information recording medium of the presentinvention, the following is provided in addition to the effect in thefirst information recording medium. Because the section of the servodata in a direction perpendicular to the read-out direction is made in astepwise form, it is possible to obtain reflection scattering lightvarying stepwise where near-field light is introduced to the servo datain each position in a direction away from a center thereof.

According to the fourth information recording medium of the presentinvention, because prepared as the servo data for tracking control are afirst groove formed having an interval increased constantly or graduallyin one direction perpendicular to both a direction of the read-out trackand a direction of a depth of the medium and a second groove madereverse in interval increase direction to the first groove, which arealternately arranged on the read-out track in the servo pattern zone.Accordingly, where near-field light is introduced to the read-out trackof the servo data in a position deviated from a center thereof, it ispossible to obtain reflection scattering light with repeating high andlow intensities. This can be utilized as a signal for tracking control.

According to the fifth information recording medium of the presentinvention, a unit of the information is constituted by a groove formedhaving a depth constantly or gradually increased in one directionperpendicular to both a direction of a read-out track to be read by thereproducing probe and a direction of a depth of the medium. Accordingly,when reading out the information, where near-field light is introducedfrom a center of this read-out track to each position perpendicular tothe read-out track and in a plane direction of the medium, it ispossible to obtain reflection scattering light different in intensity.This can be utilized as a signal for tracking.

Also, according to sixth information recording medium of the presentinvention, a section taken in a direction perpendicular to a read-outdirection to be read by the reproducing probe is formed in the form ofsaw tooth, and each slant surface constituting the saw tooth is formedwith the information as a read-out track. Accordingly, when reading outthe information, where near-field light is introduced from a center ofthis read-out track to each position perpendicular to the read-out trackand in a plane direction of the medium, it is possible to obtainreflection scattering light different in intensity. This can be utilizedas a signal for tracking.

Also, according to the first information reproducing apparatus of thepresent invention, an information recording medium is provided with areproduced-data zone recording reproduced data and a servo pattern zonerecording servo data for tracking control. The servo data is arrangedwith a constant deviation alternately left and right with respect to acenter axis of the read-out track. By making incident the near-fieldlight produced in the microscopic aperture of the reproducing probe onthe servo pattern zone, it is possible to obtain a tracking signalhaving a waveform different depending on a deviation from a center axisof the read-out track. Because the reproducing probe is controlled inposition according to the tracking signal, accurate tracking controlutilizing near-field light is made possible.

Also, according to the second information reproducing apparatus of thepresent invention, an information recording medium is provided with areproduced-data zone recording reproduced data and a servo pattern zonerecording servo data for tracking control. Prepared as the servo dataare a first groove formed having a depth increased constantly orgradually in one direction perpendicular to both a direction of theread-out track and a direction of a depth of the medium and a secondgroove formed reverse in depth increasing direction to the first groove,which are alternately arranged on the read-out track in the servopattern zone. By making incident the near-field light produced in themicroscopic aperture of the reproducing probe on the servo pattern zone,it is possible to obtain a tracking detection signal having a waveformdifferent depending on a deviation from a center axis of the read-outtrack. Because the reproducing probe is controlled in position accordingto the tracking detection signal, accurate tracking control utilizingnear-field light is made possible.

According to the third information reproducing apparatus of the presentinvention, an information recording medium is provided with areproduced-data zone recording reproduced data and a servo pattern zonerecording servo data for tracking control. Prepared as the servo dataare a first groove formed having an interval in a direction of theread-out track increased constantly or gradually in one directionperpendicular to both the direction of the read-out track and adirection of a depth of the medium and a second groove formed having aninterval in the direction of the read-out track increased constantly orgradually in the other direction perpendicular to both the direction ofthe read-out track and the direction of the depth of the medium. Theseare alternately arranged on the read-out track in the servo patternzone. By making incident the near-field light produced in themicroscopic aperture of the reproducing probe on the servo pattern zone,it is possible to obtain a tracking signal having a waveform differentdepending on a deviation from a center axis of the read-out track.Because the reproducing probe is controlled in position according to thetracking detection signal, accurate tracking control utilizingnear-field light is made possible.

According to the fourth information reproducing apparatus of the presentinvention, an information recording medium forms, as a unit of theinformation, a groove formed having a depth constantly or graduallyincreased in one direction perpendicular to both a direction of aread-out track to be read by the reproducing probe and a direction of adepth of the medium. Accordingly, when reading out the information, theintensity of the near-field light interacting with this information,i.e. a tracking detection signal detected in the photo-detector, variesin a position deviated from a center axis of the read-out track.Consequently, it is possible to control a position of the reproducingprobe according to an intensity of the tracking detection signal andperforming accurate tracking control utilizing near-field light.

According to the fifth information reproducing apparatus of the presentinvention, an information recording medium having a section taken in adirection perpendicular to a read-out direction to be read by thereproducing probe is formed in the form of saw tooth. The information isformed along a slant surface as a read-out track constituting the sawtooth. Accordingly, when reading out the information, the intensity ofthe near-field light interacting with this information, i.e. a trackingdetection signal detected in the photo-detector, varies in a positiondeviated from a center axis of the read-out track. Consequently, it ispossible to control a position of the reproducing probe according to anintensity of the tracking detection signal and performing accuratetracking control utilizing near-field light.

According to the sixth information reproducing apparatus of the presentinvention, a reproducing probe has microscopic apertures made in a formhaving an interval in a direction of the read-out track increasedconstantly in a direction of the read-out track. Accordingly, theintensity of the near-field light interacting with the informationformed on the information recording medium, i.e. a tracking detectionsignal detected in the photo-detector, varies in a position deviatedfrom a center axis of the read-out track. Consequently, it is possibleto control a position of the reproducing probe according to an intensityof the tracking detection signal and performing accurate trackingcontrol utilizing near-field light.

1. An information recording medium comprising: a read-out track having adata region forming data bits for reproduced data and a servo patternregion forming servo bits for tracking control, the servo bits having afirst groove that is deep in a direction perpendicular to both a lengthof the read-out track and a depth of the information recording medium,and a second groove that is deep in a direction opposite to the firstgroove and having a depth gradually increasing along the read-out track.2. An information recording medium as claimed in claim 1; wherein thefirst groove and the second groove are triangular in section taken inthe direction perpendicular to the length of the read-out track.
 3. Aninformation recording medium as claimed in claim 1; wherein the firstgroove and the second groove have a stepped cross-section taken in thedirection perpendicular to the length of the read-out track.
 4. Aninformation recording medium comprising: a read-out track having a dataregion forming data bits for reproduced data and a servo pattern regionforming servo bits for tracking control, the servo bits having a firstgroove extending in a direction perpendicular to both a length of theread-out track and a depth of the information recording medium, and asecond groove extending in a direction opposite to the first groove. 5.An information reproducing apparatus comprising: an informationrecording medium having on a read-out track a data region forming databits for reproduced data and a servo pattern region forming servo bitsfor tracking control, the servo bits being arranged with a constantdeviation alternately left and right with respect to a center axis ofthe read-out track; a reproducing probe for reading the read-out track,the reproducing probe having a microscopic aperture for producingnear-field light and for directing the near-field light toward theread-out track during reading of the read-out track so that thenear-field light is scattered by the servo bits formed in the servopattern region of the read-out track; photo-detecting means fordetecting reflection scattering light generated as a result of thescattering of the near-field light by the servo data and for outputtinga detection signal; comparison operating means for comparing a detectionsignal outputted from the photo-detecting means with a synchronizationsignal determined in accordance with an interval of the servo bits andfor generating and outputting a differential signal; andreproducing-probe-position control means for controlling a position ofthe reproducing probe in accordance with a differential signal outputtedby the comparison operating means.
 6. An information reproducingapparatus comprising: an information recording medium having on aread-out track a data region forming data bits for reproduced data and aservo pattern region forming servo bits for tracking control, the servobits having a first groove that is deep in a direction perpendicular toboth a length of the read-out track and a depth of the informationrecording medium, and a second groove that is deep in a directionopposite to the first groove and having a depth gradually increasingalong the read-out track; a reproducing probe for reading the read-outtrack, the reproducing probe having a microscopic aperture for producingnear-field light and for directing the near-field light toward theread-out track during reading of the read-out track so that thenear-field light is scattered by the servo bits formed in the servoregion of the read-out track; photo-detecting means for detectingreflection scattering light generated as a result of the scattering ofthe near-field light by the servo data and for outputting a detectionsignal; comparison operating means for comparing a detection signaloutputted from the photo-detecting means with a synchronization signaldetermined in accordance with an interval of the servo bits and forgenerating and outputting a differential signal; andreproducing-probe-position control means for controlling a position ofthe reproducing probe in accordance with a differential signal outputtedby the comparison operating means.
 7. An information reproducingapparatus comprising: an information recording medium having on aread-out track a data region forming data bits for reproduced data and aservo pattern region forming servo bits for tracking control, the servobits having a first groove extending in a direction perpendicular toboth a length of the read-out track and a depth of the informationrecording medium, and a second groove extending in a direction oppositeto the first groove; a reproducing probe for reading the read-out track,the reproducing probe having a microscopic aperture for producingnear-field light and for directing the near-field light toward theread-out track during reading of the read-out track so that thenear-field light is scattered by the servo bits formed in the servoregion of the read-out track; photo-detecting means for detectingreflection scattering light generated as a result of the scattering ofthe near-field light by the servo data and for outputting a detectionsignal; comparison operating means for comparing a detection signaloutputted from the photo-detecting means with a synchronization signaldetermined in accordance with an interval of the servo bits and forgenerating and outputting a differential signal; andreproducing-probe-position control means for controlling a position ofthe reproducing probe in accordance with a differential signal outputtedby the comparison operating means.
 8. An information reproducingapparatus comprising: an information recording medium containing a unitof information comprised of a groove having a depth which increasesconstantly or gradually in a direction perpendicular to both a length ofthe read-out track and a depth of the information recording medium; areproducing,probe for reading the read-out track, the reproducing probehaving a microscopic aperture for producing near-field light and fordirecting the near-field light toward the read-out track during readingof the read-out track so that the near-field light is scattered by theservo bits formed in the servo region of the read-out track;photo-detecting means for detecting reflection scattering lightgenerated as a result of the scattering of the near-field light by theservo data and for outputting a detection signal; andreproducing-probe-position control means for controlling a position ofthe reproducing probe in accordance with an intensity of the detectionsignal outputted by the photo-detecting means.
 9. An informationreproducing apparatus comprising: an information recording medium havinga groove containing a unit of information, the groove being sawtooth-shaped in a section taken in a direction perpendicular to aread-out direction, the unit of information being formed along a slantsurface of the saw tooth-shaped groove; a reproducing probe for readingthe read-out track, the reproducing probe having a microscopic aperturefor producing near-field light and for directing the near-field lighttoward the read-out track during reading of the read-out track so thatthe near-field light is scattered by the servo bits formed in the servoregion of the read-out track; photo-detecting means for detectingreflection scattering light generated as a result of the scattering ofthe near-field light by the servo data and for outputting a detectionsignal; and reproducing-probe-position control means for controlling aposition of the reproducing probe in accordance with an intensity of thedetection signal outputted by the photo-detecting means.
 10. Aninformation reproducing apparatus comprising: an information recordingmedium having a read-out track containing information; a reproducingprobe for reading the read-out track of the information recordingmedium, the reproducing probe having microscopic apertures for producingnear-field light and for directing the near-field light toward theread-out track during reading of the read-out track so that thenear-field light is scattered by the information contained in theread-out track, the microscopic apertures extending at an interval in adirection perpendicular to both a direction of the read-out track and adirection of a depth of the information recording medium;photo-detecting means for detecting reflection scattering lightgenerated as a result of the scattering of the near-field light by theinformation contained in the read-out track and for outputting adetection signal; and reproducing-probe-position control means forcontrolling a position of the reproducing probe in accordance with anintensity of the detection signal outputted by the photo-detectingmeans.
 11. An information recording/reproducing apparatus comprising: aninformation recording medium comprised of a read-out track having aslant surface and a unit of information formed along the slant surface,the read-out track being asymmetric about an axis extending in adirection generally perpendicular to a scanning direction of a probe forrecording/reproducing the unit information of the read-out track; aprobe for recording/reproducing the unit of information of the read-outtrack of the information recording medium, the probe having amicroscopic aperture for producing near-field light and for directingthe near-field light toward the read-out track so that the near-fieldlight is scattered by the unit of information of the read-out track;photo-detecting means for detecting reflection scattering lightgenerated as a result of the scattering of the near-field light and foroutputting a detection signal; and probe-position control means forcontrolling a position of the probe in accordance with an intensity ofthe detection signal or a differential signal between the detectionsignal and a reference signal.
 12. An information recording mediumcomprising: a read-out track having a servo pattern region; and aplurality of servo bits formed in the servo pattern region for trackingcontrol, the servo bits having first grooves extending deep in adirection perpendicular to both a depth of the information recordingmedium and a length of the read-out track, and second grooves extendingdeep in a direction opposite to the first grooves and alternating withthe first grooves.
 13. An information recording medium according toclaim 12; wherein each of the first grooves has a depth which graduallyincreases along the read-out track.